This kind of sensor device known from EP 611 548 A1 exhibits a round shell-type carrier in which an approximately central attachment zone is provided which is fitted with a spiral-type attachment element for attaching the carrier to the leading part of the foetus. Here, the rotational axis of the attachment element is approximately perpendicular to the surface of the carrier which is to be attached to the leading part of the foetus. The carrier also exhibits a marginal zone which can be brought into contact with the tissue of the foetus, the said marginal zone exhibiting a light emitter and a receiver. The marginal zone is formed as a spring element, whereby it presses flexibly onto the tissue of the foetus under the stressing of the spring. This ensures a reliable transmission of light from the emitter through the tissue of the foetus to the receiver, whereby good signals are obtained for evaluation.
For fitting the sensor device to the tissue of the foetus, the carrier is pressed against the tissue of the foetus and the sensor device rotated about the axis and in the rotational direction of the wire spiral, so that it screws into the galea of the foetus. The screwed-in wire spiral provides the counterpoint for the spring force with which the marginal zone presses onto the tissue of the foetus.
From U.S. Pat. No. 5,199,432 and U.S. Pat. No. 5,373,843 it is known that a cylindrical CTG sensor (cardiotocography) is provided at its front end with a wire spiral and is fastened by the wire spiral penetrating into the tissue of a person. For fitting, the cylindrical sensor is joined at its rear end to a rotating bar which is supported for rotation in a tube. The leads leaving the sensor extend longitudinally through the hollow space of the rotating bar and are brought out at the back.
When feeding in the sensor, the sensor is first arranged withdrawn inside the tube. Once the tube is placed on the human tissue, the sensor is pushed axially towards the front with the aid of the rotating bar and then twisted. The problem arises in that the handling of the leads running through the rotating bar and the tube is cumbersome in practice, in particular when the sensor is fitted to the tissue and the rotating bar and the tube are withdrawn when they are no longer required.
An analogous method of attachment with a wire spiral is suggested in U.S. Pat. No. 4,644,957 with which the same problems arise. With these sort of arrangements there is also the disadvantage that the tubes are often filled with amniotic fluid which contaminates the leads and plug contacts. Due to the electrolyte content of the amniotic fluid, an electrically conductive film remains which can negatively affect the sensor signals.
U.S. Pat. No. 6,058,321 describes a measurement appliance for the continuous monitoring of a foetal electrocardiogram and for the intermittent monitoring of a blood pH value of the foetal scalp during a delivery. A spiral-shaped needle for screwing into the scalp protrudes from a flat bottom of the appliance. A hollow needle of the pH probe is stored withdrawn within the appliance during the screw-in process, so that it has no contact with the tissue of the foetus. A rotatable retention ring with a receiving recess for the hollow needle of the pH probe is arranged around the base element, the said retention ring being locked onto the base element when the spiral needle is screwed in. When the spiral needle is securely attached in the scalp of the foetus, the pH probe with the retention ring can be screwed in at various spaced measurement positions from which the hollow needle of the pH probe can be extended to extract a blood sample from the foetal scalp.